Soil quality indicators as influenced by no-tillage, conventional tillage and nitrogen fertilization after 3 years of continuous maize in the Po Valley

The technique of no-tillage (NT) has never been applied over a large area in Italy, especially for maize (Toderi and Bonari, 1986; Bartolini, 1989; Caliandro et al., 1992). Nowadays it is probable that a total of about 55 000 ha are cropped under NT, the prevalent crops being autumn-winter cereals, soybean and sunflower, with only a thousand hectares devoted to maize Tabaglio, 2007). The limited use of this land management technique is due to several factors: wrong choice of soil-type, short-term experimental studies, and inadequate basic knowledge of the various herbicide treatments and fertilizers needed. Overall though, the limited adaptability of farmers to the new principles of management necessary for NT has been the major obstacle. Nevertheless, the advantages and conditions for the application of NT have been repeatedly presented and discussed worldwide (Phillips and Phillips, 1984; Sprague and Triplett, 1986; Bartolini, 1989; Baker et al., 2006; Tabaglio and Gavazzi, 2006; Pisante, 2007). More specifically, in the absence of the plough the soil profile is undisturbed and the environment is less oxidative, the most important consequence being an improvement in soil quality and health over time. The most appropriate techniques to detect and to measure this improvement need to be identified. Given that a single parameter cannot describe the complexity of the soil ecosystem, it becomes necessary to establish how many and which soil quality indicators to use (Doran and Parkin, 1994; Larson and Pierce, 1991; Benedetti and De Bertoldi, 2000; Dell’Abate, 2000; Landi et al., 2000; Vignozzi, 2000). For this research, chemical (pH, electrical conductivity, organic matter, total nitrogen, available phosphorus, exchangeable potassium, cation exchange capacity and carbonates) and physical (water aggregate stability) indicators were considered. The aim of this field experiment was to verify the ability of these indicators to detect any changes in soil quality in relation to changes in tillage management and different levels of nitrogen fertilization, after three years of continuous maize.